Please refrain from commenting just "thank you" on answers. Thank them by upvoting. If you have something else to say it, great, do so but just saying thanks is clutter and will likely be deleted.
– Catija♦Oct 30 '16 at 22:55

From the opposite end - why would a top actor want to do something different? Variety? To avoid being typecast in a specific role? To do something fun that doesn't express the same requirements as physical acting? Acting that is more cerebral? Availability-voice acting takes a lot less time, and could fit in before his next scheduled role? Vin Diesel probably has enough money to indulge himself.
– CriggieOct 31 '16 at 0:08

4

As my comment was supposed to indicate, it's not about how much I like him or don't. But he is a niche actor, he's not got the breadth of roles I would expect an A lister to have. With the exception of Riddick, it's hard to credit him with all of the draw on the box. He doesn't have the kind of draw or range that someone like DiCaprio or Will Smith have, that's all I was trying to say. If you google "a list actor list" there's even a scroll bar of them, that doesn't include him.
– PaulOct 31 '16 at 21:26

All of the 'I am Groots' that were earlier voices didn't sound very
good at all, they sounded like shit. It just didn't really work.

Then
Vin came in and in one day, laid down all these 'I am Groot' tracks,
and he's a perfectionist. He made me explain to him with every 'I am
Groot,' exactly what he was saying …

Then Vin would sit there and he
would do it and he would it again and again and again, and his voice
is so rich and so beautiful and he really opened up and was this
character. It was amazing when we first put that voice in there how
much the character changed and how much he influenced the character.

I was lucky that I had a director [James Gunn] who was willing to
indulge me. I told him:

‘We know that Groot is really saying any
number of things when he says that line and most people are oblivious
to the nuances of his speech because of his hardened larynx’.

All you
hear is the growl but he could be saying any number of things and we
know that Rocket Raccoon understands him. He doesn’t always tell
everybody he understands Groot and he plays on that, but he does
understand him.

So I asked James:

‘Can you give me a basic idea of
what he’s trying to say when he’s saying “I am Groot”?’

James had a
50-page document waiting for me when I came in to do the voice. On the
left-hand side of the page it said ‘I am Groot’ and on the right-hand
side it had whatever the line really was if you could understand this
floral colossus. That was the beginning of trying to go deep into a
character like this.

In many ways it was the most challenging thing to
ask an actor to do. The thespian in me responded to the challenge of
not being able to use facial expressions, physicality or a Golum-like
vocabulary.

Remember that Vin Diesel was the voice actor for the Iron Giant in The Iron Giant (1999), and it was a great role which his unique voice suited, so we know that Vin Diesel is not just an A List actor that happens to be voice acting for Groot, but that he is actually a good voice actor with the resume to back it up.

As for hiring any A lister actor to voice act in your movie, any opportunity for a studio to put a famous actor's name on a poster (ensuring more ticket sales) is one they will always take. Starpower translates directly to more successful box office sales, and Vin Diesel, especially around the time of Guardians of the Galaxy releasing, was immensely popular.

Side-note: he is also a prolific voice actor for video games, including the Chronicles of Riddick franchise games based on his character Richard B. Riddick from the film Pitch Black (2000), and a Grand Theft Auto style game called Wheelman. He seems to love video games, tabletop games and other aspects of geek culture, which makes him an adequate fit for an obscure comic book movie.

Riddicks first name is Richard? I'd never heard of that before. "Riddick" is the name of a kick-ass anti-hero, whereas "Richard B. Riddick" sounds like an accountant, and not a very good one at that.
– user11607Oct 30 '16 at 22:42

Let’s not forget that much of what an actor does comes in the form of how he says his lines. Most of communication occurs outside of just words. Much of that is in motions and gestures, but much of it is also in intonation, timing, stress, volume, etc. Plus, Vin Diesel has a unique sounding voice that fits the role of a large, powerful tree being.

Some reinforcing points for thought are these. One of the shortcomings of email is you simply receive the words someone says, and lose much of the full meaning coming from the sender. Another example close to home for me is when you talk to your pet. They don’t understand language for the most part, but they understand a lot based on how you speak it.

As far as an A-list actor goes, the handicap of only speaking several actual words means that your full acting talent has to come to bear in order to pull it off. Maybe an A-lister is what is needed here. By the way, Groot also says “We are Groot”.

thank you for your thoughts. the comparing to the animals and humans is pretty interesting and a valid thought. and yes. i remember that he does changed the sentence at the end. but i'm currently in the middle of the movie :)
– David SeekOct 30 '16 at 7:01

8

This pretty much nails it: "the handicap of only speaking several actual words means that your full acting talent has to come to bear in order to pull it off". Conveying the right, but varying, things with the same text is hard.
– MastOct 30 '16 at 9:25

Also, getting even an A-lister to go into a sound booth and say "I'm Groot" repeatedly is relatively inexpensive and adds a recognizable name to the cast which will draw a larger audience.
– John SensebeOct 30 '16 at 12:34

@JohnSensebe "relatively inexpensive"According to many reports, Diesel earned approximately $25 million for his acting work on Guardians and Furious 7
– Ghoti and ChipsOct 31 '16 at 12:36

2

Also, don't forget that he voiced for Groot in many different languages, as many as 15 languages. I doubt that the cost of that was "inexpensive", even if we're speaking relatively.
– Ghoti and ChipsOct 31 '16 at 12:39

In theater, there is a very famous scene in the play "Cyrano De Bergerac" in which the titular character repeats a single word over and over (twenty times or so?). It's considered a real challenge for an actor to perform this scene well -- because you have to find some way of making each repetition something different that adds to the scene.

There's a similar scene in a more recent play called "Peter and the Starcatcher" in which a character repeats the phrase "ohmigod" dozens of times, rapid fire. Done well it's hysterically funny. Done poorly, the joke would have fallen completely flat.

Or another play, "The Foreigner", in which one character tells a story in a gibberish made-up language. The ENTIRE scene only makes any sense (and again, can be quite funny) if there person playing the role does it well. With a lesser actor you're basically just watching someone go "blah blah blah" for five minutes and it would be terribly unfunny.

Having the single line "I am Groot" was NOT a simple thing to do well. I actually give Vin Diesel a lot of credit for the performance he gave. He managed to make a character with one line (okay... two lines) compelling and entertaining. He earned his paycheck.

For big budget films and from a business perspective big name stars are a good way to help ensure a good return on investment.

Also consider that Vin Diesel has a fairly well defined persona which audiences are familiar with and for a character like Groot especially this can be an effective and efficient way to give a character a bit more depth and relatability.

Similarly it is not trivial to create a convincing CGI charter or puppet from scratch and having a real actor to work with who is capable of capturing the personality of that character can help a lot. Consider also the physical acting work that Andy Serkis did for Gollum which undoubtedly helped to sell the character on screen in a way that a random person acting as a motion capture placeholder probably would not have managed in part through interaction with actors, animators etc that you never see on screen.

As far as I understand it - Diesel was in talks to star in Inhumans; but when Marvel saw the fan reaction to him joining the MCU, they didn't want to wait that long; and started looking for a role he could do sooner:

Thank you for your interest in this question.
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